How UCT in MCTS selection phase avoids starvation?
First explore the nodes A,B,C once.
For reference see this paper by David Silver and Sylvain Gelly, Combining Online and Offline Knowledge in UCT

If any action from the current state $s$ is not represented in the tree, $\exists a \in \mathcal{A}(s),(s, a) \notin \mathcal{T},$ then the uniform random policy $\pi_{\text {random }}$ is used to select an action from all unrepresented actions, $\tilde{\mathcal{A}}(s)=\{a \mid(s, a) \notin \mathcal{T}\}$.